Brainstem & Diencephalon · 2019-02-04 · Brainstem Functions •Ascending and descending tracts...
Transcript of Brainstem & Diencephalon · 2019-02-04 · Brainstem Functions •Ascending and descending tracts...
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Brainstem & Diencephalon
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Lecture Objectives• Identify the gross features of the brainstem.• Briefly describe the internal structure of the brainstem (ascending
and descending pathways, sensory and motor cranial nuclei, substantia nigra, red nucleus, olivary nucleus and reticular formation).
• Describe the main connections of the sensory cranial nuclei.• Describe the main connections of the motor cranial nuclei.• Review the blood supply of the brainstem.• Describe lesions in the brainstem such as medial medullary
syndrome and lateral medullary syndrome.• Describe the main connections of the substantia nigra and the red
nucleus.• Describe the main connections of Reticular Formation and
correlate these connections with its main functions.• Describe the anatomical features of the diencephalon;
components, location and relations.
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Principal Parts of the Brain
• Cerebrum• Diencephalon
– Thalamus, hypothalamus & epithalamus
• Cerebellum• Brainstem
– medulla, pons & midbrain
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Brainstem Functions
• Ascending and descending tracts• Reflex centers
– Cardiovascular and respiratory centers– Coughing, sneezing, swallowing
• Nuclei of the cranial nerves–Motor and sensory
• Consciousness and arousal
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External Anatomy of Brainstem: Ventrally
• Midbrain – Cerebral peduncles (basis pedunculi)
– Interpeduncular fossa
• Pons – Basilar pons – Basilar sulcus
Bulbopontine sulcus• Medulla oblongata
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External Anatomy of Brainstem: Ventrally
Bulbopontine sulcus• Medulla oblongata
– Ventral median fissure– Pyramids– Decussation of pyramids– Olives– Pre‐olivary & post‐olivary sulci
– Inferior cerebellar peduncles
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External Anatomy of Brainstem: Dorsally
• Corpora quadrigemini(midbrain)– Superior & inferior colliculi
• Cerebellar peduncles– Lateral walls of 4th ventricle
• Gracile & cuneatetubercles (closed surface of medulla)– Inferior to 4th ventricle
• Rhomboid fossa– Pontine part– Medullary part (open
medulla)
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Rhomboid Fossa• Posterior median sulcus• Medial eminence (pons)• Facial colliculus
– Caudal part of the eminence• Sulcus limitans• Striae medullares• Trigons
– Vagal trigon (more lateral‐inferior)– Hypoglossal trigon (more medial‐
superior)• Vestibular areas
– Lateral points of the fossa• Isthmus – superior constriction• Obex – inferior narrowing
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Brainstem Structureventral middle dorsal
Basis peduncularis
tegmentum
Tectum
Basis pontis
Cerebellum
Pyramids
Midbrain
Pons
Medulla
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Functional Distribution of Brainstem Nuclei
Midline – GSE – III, IV, VI, XII – SVE – V, VII, IX, X, XI– GVE – III, VII, IX, X
Sulcus limitans– GVA – n. of tractus solitarius– SVA – n. of tractus solitarius– GSA – V sensory nuclei– SSA – vestibular & cochlear
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Brainstem Nuclei
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Brainstem Nuclei
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Internal Structures of Medulla
• Level of pyramidal decussation (closed part)– Cranial nerve nuclei
• Spinal tract & nucleus of trigeminal nerve
– Motor pathways• Pyramids
– Decussation of pyramids
– Somatosensory pathways• Nucleus gracilis & cuneatus• Fasciculus gracilis & cuneatus
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Internal Structures of Medulla
• Level of internal arcuatefibers (closed part)– Cranial nerve nuclei
• Spinal tract & nucleus of trigeminal nerve
– Motor pathways• Pyramids
– Somatosensory pathways• Fasciculus gracilis & cuneatus
• Nucleus gracilis & cuneatus• Internal arcuate fibers
– Decussation
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Internal Structures of Medulla
• Level of olivary nucleus (open part)– Cranial nerve nuclei
• Hypoglossal nucleus• Dorsal vagal nucleus• Vestibular nuclei• Nucleus of tractus solitarius• Spinal tract & nucleus of
trigeminal nerve– Motor pathways
• Pyramid• Olivary nucleus• Inferior cerebellar peduncle
– Somatosensory pathways• Medial lemniscus
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Internal Structures of the Pons
• Caudal part– Cranial nerve nuclei
• Nucleus of abducentnerve
• Motor nucleus of facial nerve
– Motor pathways– Somatosensory pathways• Medial lemniscus
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Internal Structures of the Pons
• Cranial part– Cranial nerve nuclei
• Motor nucleus of trigeminal nerve
• Main sensory nucleus of trigeminal
– Motor pathways• Middle & superior cerebellar peduncles
• Pontine nuclei• Corticospinal fibers
– Somatosensory pathways• Medial lemniscus
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Internal Structures of the Midbrain
• Level of inferior colliculi– Cranial nerve nuclei
• Nucleus of trochlear nerve• Mesencephalic nucleus of trigeminal nerve
– Motor pathways• Inferior colliculi• Decussation of superior cerebellar peduncles
• Substantia nigra• Crus cerebri
– Somatosensory pathways• Medial lemniscus
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Internal Structures of the Midbrain
• Level of the superior colliculi– Cranial nerve nuclei
• Nucleus of oculomotor nerve
– Motor pathways• Superior colliculi• Red nucleus• Substantia nigra• Crus cerebri
– Somatosensory pathways• Medial lemniscus
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Spinal cord & Brainstem Labeled Sections: External Link
• http://www.bellarmine.edu/faculty/mwiegand/atlas/cover.html
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Blood Supply to Brainstem• Blood supply to BS is from
posterior circulation• Vertebral a.
– Anterior spinal a.– PICA
• Basillar a.– AICA– Paramedian branches– Circumferential branches
• Short & long– SCA– PCA
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Blood Supply to Brainstem
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Blood Supply: Medulla
• Anterior spinal a.• Vertebral a.• PICA
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Medullary Lesions
Medial medullary syndromeLateral medullary (Wallenberg) syndrome
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Blood Supply: Pons • Caudal pons
– Basilar a. • Paramedian• Circumferential
– AICA
• Rostral pons– Basilar a.
• Paramedian• Circumferential
– SCA
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Blood Supply: Midbrain• Paramedian branches (Basilar a.)
• PCA– Quadrigeminal
• SCA
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Midbrain Lesions
Weber’s syndrome Benedikt’s syndrome
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Signs/symptoms Affected structures
Weber’s syndrome Ipsilateral CN III palsyContralateral hemiplegia
CN IIICrus cerebri
Benedikt’s syndrome Ipsilateral CN III palsyContralateral tremorContralateral hemianesthesia
CN IIIRed nucleusMedial lemniscus
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Reticular Formation
• Scattered nuclei in medulla, pons & midbrain• Lateral one third have small cells (parvocellular)– Receive sensory inputs and cortical inputs
• Medial two thirds have large cells (magnocellular)– Output to spinal cord, brainstem nuclei, thalamus, hypothalamus & cerebral cortex
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Reticular Formation Functions
• The reticular formation modulates (excite or inhibit) the activities of:– Sensory systems – e.g. pain–Motor systems – e.g. muscle tone, segmental reflexes, eye movements
– Autonomic systems – e.g. respiration, blood pressure, cardiac function
– Consciousness – e.g. vital centers in the brainstem, awareness, attention & arousal
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Organization of Reticular Formation• Reticular formation organized into three longitudinal columns–Midline raphe group– Parasagittal medial zone– Parasagittal lateral zone
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Organization of Reticular Formation
• Fourth set of nuclei that have common cerebellar projections (precerebellarreticular nuclei)Coordination of muscle contraction
– Paramidian reticular nucleus of the medulla
– Lateral reticular nucleus of the medulla
– Reticulotegmental nucleus of the pons
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Raphe Nuclei• Serotonin projecting cells• Rostral group (upper pons & midbrain)– Project to cerebellum, cerebrum (cortex, basal ganglia, limbic system)
– Involved in the regulation of forebrain activity• Sleep, memory processing, mood
• Caudal group (lower pons & medulla)– Receives nociceptive input from brainstem & spinal cord • Involved in the regulation of pain
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Medial Reticular Zone• The effector part of the reticular formation
– Provides most of the ascending & descending projection• Most inputs come from the lateral reticular zone (sensory somatic
& visceral)• Ascending projections form the Ascending Reticular Activating
System (ARAS)– Alter the levels of consciousness & state of attention
• Conscious activities of the cerebral cortex require excitatory influences from the ARAS
• Descending projections regulate muscle tone, spinal reflexes & motor activity through – Medial (pontine) reticulospinal tract
• ↑ muscle tone spinal reflexes– Lateral (medullary) reticulospinal tract
• ↓ muscle tone spinal reflexes
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Medial Reticular Zone
• Locus ceruleus in pons– contain norepinephrine & extensive projections throughout CNS
– Ascending projections are part of the ARAS• Involved in the mood, memory and regulation of motor activity
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Lateral Reticular Zone
• Receives extensive afferents to mediate cranial nerve reflexes and visceral functions
• Output is mainly to medial zone• Other projections
– Pedunculopontine nucleus (acetylcholine neurons)• Projects to the substantia nigra, subthalamic nucleus, motor cortex, & medial zone– All have important motor control functions
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Organization of Reticular FormationNeurotransmitter Distribution
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Reticular Formation: Neurotransmitter Pathways & Functions
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The Diencephalon
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Thalamus: Structure
• From medial to lateral:– Medial n.
• Dorsomedial n.
– Anterior n. Internal medullary lamina
Intralaminar n.
– Lateral n. External medullary lamina– Reticular n. Internal capsule
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Thalamus: Lateral Nucleus• Subdivided into:
– Dorsal tier• Lateral dorsal (LD)• Lateral posterior (LP)• Pulvinar (Pu)
– Ventral tier• Ventral anterior (VA)• Ventral lateral (VL)• Ventral posterior (VP)
– Ventral posterolateral (VPL)– Ventral posteromedial (VPM)
• Posterior nucleus (Po)– Medial & lateral geniculate
nuclei
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Specific Nuclei
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Non‐specific Nuclei
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Hypothalamus
• Location• Boundaries
– Lamina terminalis– Hypothalamic sulcus– 3rd ventricle
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Hypothalamus: Nuclei
• Divisions – In coronal section
• Periventricular • Medial Fornix • Lateral
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Hypothalamus: Nuclei
• Divisions– In sagittal section– Chiasmatic (anterior, supraoptic)
– Tuberal (middle)– Mamillary (posterior)
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Hypothalamus: Function
Hypothalamus
Neural influences Hormonal influences
Autonomic NS Limbic S Endocrine S
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Hypothalamus: Nuclei & Functions
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Limbic System
• Involved in complex behaviors– To preserve life – Motivation– Emotions– Affective behavior– Memory
• Includes– Cingulate gyrus– Parahippocampal gyrus– Mamillary bode– Hippocampus– Anterior & dorsomedial thalamic nuclei
– Amygdala– Septal nuclei– Nucleus accumbens– Substantia inominata
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Limbic System: Components
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Limbic System: Circuit of Papez• Thought to have role in emotions, motivation & affective behavior